1. Field of the Invention
The present invention relates to a sheet feeding apparatus for feeding sheets.
2. Description of the Related Art
A sheet feeding apparatus for feeding sheets is used in, for example, a recording apparatus that executes recording on recording sheets. There are various types of recording apparatuses for recording on recording sheets, including an ink jet recording apparatus. Among the various recording apparatuses, the ink jet recording apparatus has popularly been used, as it is inexpensive and capable of recording high-quality images on large roll paper.
When roll paper is set in the ink jet recording apparatus, if a leading edge portion of the roll paper is inserted straight with respect to the conveyance direction of conveyance rollers, recording will be normally executed. On the other hand, if the leading edge portion of the roll paper is inserted in a skewed state, the roll paper will not be conveyed straight to cause an image to lie outside the roll paper, resulting in defective recording. A technique to overcome this problem is discussed in Japanese Patent Application Laid-Open No. 2007-245352. Specifically, the width of roll paper is detected at the time of sheet feeding operation executed prior to recording operation, and based on the detected data, if it is determined that defective recording is likely to occur, a message is displayed to prompt the user to reset the roll paper.
In the foregoing technique, the user opens a nip releasing lever for conveyance rollers, inserts roll paper, aligns side edges of the roll paper with a mark indicated on a sheet discharge unit, and then closes the releasing lever to nip the rollers. Then, a reflection type sensor mounted on a carriage, which moves in a direction that is perpendicular to the conveyance direction, measures a position X1 of the sheet side edge. Thereafter, the roll paper is conveyed by about 300 mm, and then a position X2 of the sheet side edge is measured. A difference between the positions X1 and X2 is calculated to obtain a skew amount of the sheet. If the calculated skew amount is smaller than a threshold value, which means that the skew amount is acceptable for recording, the sheet feeding operation is completed. On the other hand, if the skew amount is larger than the threshold value, an error message is displayed to prompt the user to reset the roll paper.
The foregoing technique uses manual sheet feeding. In manual sheet feeding, a user releases the nip of conveyance rollers and aligns a sheet to a mark. In recent years, however, automatic sheet feeding has increasingly been used to reduce user inconvenience. In automatic sheet feeding, a leading edge portion of roll paper is automatically drawn by conveyance rollers. Examples of a method of automatic sheet feeding include a method in which when a sensor disposed near conveyance rollers has detected a leading edge portion of roll paper, the conveyance rollers start rotating. Another example is a method in which when a leading edge portion of roll paper has been inserted between a pair of rollers released from a nip state, the pair of rollers automatically shifts to the nip state to convey the roll paper.
In the automatic sheet feeding, operation procedures are simplified compared with the manual sheet feeding. However, a leading edge portion of roll paper may be drawn before the user thoroughly checks the skew of the roll paper. Thus, the initial skew variability is greater than that in manual sheet feeding. Accordingly, use of a method such as the technique discussed in Japanese Patent Application Laid-Open No. 2007-245352 in which whether image recording can be executed is determined based only on the skew amount of the roll paper may result in frequent error displays. Consequently, the number of times that resetting of the roll paper is required increases to cause user inconvenience. To overcome this problem, an operation is executed to prevent roll paper from being skewed. Specifically, after a leading edge portion of the roll paper is drawn, back tension is applied to the roll paper, and then the roll paper is conveyed by a certain distance (for example, 300 to 400 mm), whereby the skew is reduced. The skew amount is measured thereafter so that the frequency of error displays can be reduced.
However, if the user sets roll paper such that the roll paper is extremely skewed, a leading edge portion of the roll paper may hit a side wall of a conveyance path while being conveyed for skew detection, leading to a paper jam. On the other hand, if the conveyance distance of the roll paper is decreased to avoid a paper jam, the skew detection accuracy decreases to cause a problem of frequent skew errors.